In recent years, a semiconductor device typified by a thin-film transistor (TFT) has been used for various applications such as liquid crystal, other display devices or solar cell panels. The semiconductor device predominantly used at present, and in particularly a semiconductor device using silicon as a semiconductor material, suffers from high production cost, because a vacuum process such as CVD and sputtering is employed when manufacturing. Also, in view of the process temperature, it is difficult to produce such a semiconductor device as a flexible device formed on a polymer film or the like.
In the field requiring low cost, such as in the field of lightweight flexible device and RF-ID (Radio Frequency Identification) which are expected to be used in the future, studies are being made to apply an organic semiconductor device manufacturable by a simple and easy method to an active device. The vacuum deposition apparatus or coating apparatus used in the manufacture of such an organic semiconductor device is inexpensive compared with the CVD apparatus or sputtering apparatus used in the manufacture of an inorganic semiconductor. Furthermore, in the manufacture of an organic semiconductor device, the process temperature is low, and therefore it is also possible to form the organic semiconductor device on a polymer film, paper or the like.
A thin-film transistor using an organic semiconductor has, on a substrate, a source electrode, a drain electrode, a gate electrode, a gate insulating film and an organic semiconductor film. In such a thin-film transistor, the source electrode and the drain electrode are insulated from the gate electrode by the gate insulating film, and thereby the current flowing from the source electrode to the drain electrode through the organic semiconductor is controlled by the voltage applied to the gate electrode.
The organic semiconductor film is an aggregate of a low molecular compound or a polymer compound. As the organic semiconductor material of a low molecular type, for example, an acene-based compound (a condensed polycyclic compound where rings are linearly fused) such as pentacene and thiophene oligomer is known. Also, as the organic semiconductor material of a polymer type, a regioregular polyalkylthiophene (P3AT) and a poly(fluorenebithiophene) (F8T2) are known.
In order to obtain high switching characteristics in an organic thin-film transistor, the charge mobility of the organic semiconductor film must be enhanced. As the method for enhancing the charge mobility of the organic semiconductor film, highly aligning organic semiconductor molecules forming the organic semiconductor film is commonly carried out. For the formation of a highly-aligned organic semiconductor film, it is known to surface-treat the substrate or gate insulating film, on which the organic semiconductor film is deposited, and particularly to cover the gate insulating film surface, on which the organic semiconductor film is deposited, with a Self-Assembled Monolayer (SAM) (Patent Documents 1 and 2 and Non-Patent Documents 1 to 3).
As the substrate or gate insulating film, on which the organic semiconductor film is deposited, a silicon oxide thin film can be used. As the SAM covering the substrate or gate insulating film an organosilane monolayer, for example an alkylsilane monolayer, can be used.
When an organic semiconductor is formed on a substrate or gate insulating film previously surface-modified with SAM, the charge mobility of the organic semiconductor film is enhanced. According to this technique, an organic TFT having charge mobility surpassing that of the existing TFT composed of amorphous silicone has been also reported.
In this connection, various techniques for reforming a substrate surface having OH groups such as silica surface with SAM such as organosilane layer (silane coupling agent layer) are known (Non-Patent Document 4). Known representative forming methods include a solution method of performing a silane coupling reaction between OH groups on the substrate and organosilane in a solution, and a vapor phase method of performing the reaction in a vapor phase by using an organosilane vapor. Regarding the solution method, it is known that SAM having high flatness is obtained by performing the silane coupling reaction in a solution with a low water content (Non-Patent Document 5).
Also, it is known to form an organosilane thin film by using a microcontact printing method (Non-Patent Document 6). In this case, a patterned organosilane thin film may also be formed by coating organosilane as a coupling agent on a patterned stamp, and transferring the coupling agent onto a substrate.